This invention relates to a secondary air guide ring for an ignition plug and, more particularly, to one which is mounted on the ignition plug such as to permit effective scavenging of residual gas in an internal combustion engine such as a gasoline engine and also promote complete combustion of the combustion gas.
The residual gas in the cylinder of an internal combustion engine generally reduces the average effective pressure in the cylinder, charging efficiency and so forth and increases the temperature within the cylinder, and thus the temperature and weight of the residual gas has great influence upon the engine performance.
In particular, it has been found that the pressure of the combustion gas within the cylinder locally assumes values lower than the atmospheric pressure, that is, becomes negative pressure, in the intake stroke and power and exhaust strokes.
This phenomenon of reduction of the pressure of the combsution gas is observed in a variety of internal combustion engines such as gasoline engines, diesel engines and rotary engines, and it is thought to stem from the fact that combusted gas consumes oxygen at the time of propagation of flame. Accordingly, various attempts have hitherto been made to reduce the weight and temprature of the residual gas by blowing secondary air into the cylinder. As a result of these attempts, the inventor has developed an ignition plug having a check valve mechanism. In this ignition plug, the center electrode of the positive electrode body is provided with an air guide passage communicating the inside and outside of the cylinder, and a check valve for preventing the counter flow of gas in the cylinder is provided in an intermediate portion of the air guide passage. Since this construction permits the afore-mentioned secondary air introducing method to be realized without substantially changing the main portion of the engine, its utility is expected.
However, since in the afore-mentioned ignition plug the air guide passage and check valve mechanism are assembled in the center electrode of a very small diameter, the manufacture is very difficult compared to the conventional plug, thus leading to high cost, and also the structure has low mechanical strength and short service life.
Further, it has been proved by experiments conducted by the inventor by trial manufacturing the afore-mentioned ignition plug and mounting it on an engine, that the afore-said check valve on-off operates for introducing air in accordance with the engine rotation at the time of low speed operation of idling operation of the engine, in case of high speed operation or under high load the valve no longer on-off operates according to the engine rotation and counter flow of air-fuel mixture into the passage is caused to cause abnormal explosion in the inside, thus causing extreme wear of the ignition plug itself and also causing great noize accompanying the on-off operation of the valve.
This is attributable to the fact that the valve stroke of the check valve is so large that air in excess of the required quantity is introduced into the engine. However, since the afore-mentioned air guide passage must extend through the center electrode in the longitudinal direction thereof in view of the construction of the ignition plug, it has inevitably a length. Therefore, its diameter has to be extremely small. In addition, in case if the check valve itself is very small, the function of introducing secondary air cannot be obtained at all.
From the above grounds, although the method of secondary air introduction by using the afore-mentioned ignition plug has the above advantages, it does not permit expected effects to be obtained and thus has not been used in actual practice up to date.